1. Field of the Invention
The present invention relates to a signal detection circuit.
2. Description of the Related Art
There is known a fluxgate magnetometer utilizing nonlinear magnetization characteristic of a ferromagnet. There is known, as an example, a fluxgate magnetometer configured with an exciting coil drive circuit, a magnetic sensor, and a signal detection circuit of the magnetic sensor (see Japanese Patent Application Laid-Open Publication No. 2007-78423).
A signal detection circuit of this magnetic sensor periodically saturates a magnetic flux of the exciting coil in the magnetic sensor with a periodic drive signal input from the exciting coil drive circuit to detect an induced voltage waveform of an induced detection coil in the magnetic sensor by variations in density of the magnetic flux. When an external magnetic field is applied, since saturation time intervals are varied depending on intensity of the external magnetic field, information about direction, etc., of the external magnetic field can be obtained by counting adjacent intervals of the detected voltage waveform with a counter including in the signal detection circuit of the magnetic sensor.
Since the fluxgate magnetometer measures a plurality of magnetic fields relative to a spatial axis direction, a multiplicity of direction data are required to be handled. Therefore, a highly accurate counter is required to be included in the signal detection circuit of the magnetic sensor to obtain information of the external magnetic field.
However, since the signal detection circuit of the magnetic sensor is required to be highly accurate and stable at the same time, when preparing the highly accurate counter, there is a problem that an increase in the number of constituent bits of a counter or an increase in frequency of a clock signal are inappropriate because generation of noises, an increase in cost, etc., are caused.